In an image forming apparatus such as a copy machine and a printer, a fixing device is used that heats a heating rotating body such as a fixing belt including a conductive layer (a heat-generating layer) that generates heat by an electromagnetic induction heating (IH) device. Such a fixing device includes an auxiliary heat-generating member disposed to be in contact with the heating rotating body.
When the temperature thereof is lower than the Curie temperature, the auxiliary heat-generating member exhibits ferromagnetism and heats the fixing belt by forming a magnetic path. On the other hand, when the temperature exceeds the Curie temperature, the auxiliary heat-generating member is changed from the ferromagnetism to paramagnetism, and the magnetic path is not formed therein, whereby the fixing belt is not heated. Since the magnetic member is formed of a magnetic shunt alloy, a temperature rise in the fixing belt is facilitated when the temperature is low and excessive heating on the fixing belt is suppressed when the temperature is high with the Curie temperature as a boundary. Further, in such a fixing device, a thermostat operating depending on the temperature of the auxiliary heat-generating member is used together therewith. The thermostat is disposed to be in contact with the auxiliary heat-generating member, and operates when the temperature of the fixing device becomes higher than a predetermined temperature, thereby interrupting power supply to the IH device.